The ability to change the position of the keyframes in a collapsed view.

Imagine that you have a way to see if an object has or not a keyframe in a specific position. This can be helpfull to select a range and move it in the timeline. It is not to change properties, only position (therefore duration)

You can click on the triangle on the left to see (and edit) the global keyframes (red elipses), and you can select just some of them (red rectangle), this will select in reality all keyframes in that time segment (orange rectangle)